JPH09183753A - Esterification of (meth)acrylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for esterifying (meth)acrylic acid in the presence of an esterification catalyst using an alkanol by removing un reacted starting materials and produced a (meth)acrylic acid ester by a distillation and also obtaining a residual product containing an oxyester.

SOLUTION: This method for esterifying (meth)acrylic acid is to separate and remove a residual products, also mix the residual products directly with (meth)acrylic acid, also dissociate an oxyester presenting in the residual product at an elevated temperature in the presence of an acid catalyst, or separate the oxyester first from the residual products by a distillation, mix the distillate with (meth)acrylic acid and dissociate at the elevated temperature in the presence of the acid catalyst. By this method, it is possible to attain a higher conversion rate than that of the known method and also the loss of the starting material is less than that of the known method.

COPYRIGHT: (C)1997,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an esterification catalyst by separating unreacted starting compounds from the produced (meth) acrylic acid ester by distillation and obtaining a residual product containing an oxyester. To a method of esterifying (meth) acrylic acid with an alkanol in the presence of In the context of the present invention, the term (meth) acrylic acid customarily means acrylic acid or methacrylic acid.

[0002]

The preparation of alkyl esters of (meth) acrylic acid is usually carried out using alkanols at elevated temperature in the liquid phase in the presence or absence of solvents, in the presence of acids as catalysts ( It is carried out by esterifying (meth) acrylic acid (German Patent Application Publication No. 233).
9519). The disadvantage of this process is that a second reaction takes place under the esterification conditions mentioned above, i.e. the still unreacted starting alcohol is already formed (meth).
By adding to the double bond of an alkyl acrylate (Michael addition), the general formula I:

[0003]

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The compound of the general formula II is formed by adding the compound of formula ## STR1 ## and still unreacted (meth) acrylic acid to the double bond of the ester formed.

[0005]

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[In the above two formulas, x and y represent 1 to 5, R represents an alkyl group, and R ′ represents an H atom or CH ₃
Represents a group and R'represents an H atom, esterification is esterification of acrylic acid, and R'represents a CH ₃ group, esterification is esterification of methacrylic acid] A compound is produced. Multiple additions are possible as well. In the case of addition, mixed types can occur. These adducts (alkoxy esters and acyloxy esters) are abbreviated as oxyesters.

The problem of oxyester formation is that in the case of the production of esters of acrylic acid, the major oxyesters produced are alkoxypropionate and acyloxypropionate where x and y are 1. , Especially serious. In the production of esters of methacrylic acid, oxyester formation occurs to a lesser extent. The production of oxyesters is described in DE-A-2339529. This published German patent application points out that the formation of the oxyester occurs essentially independently of the particular esterification conditions. C ₁ -C ₈ - alkanols, especially C ₄
-C ₈ - In the preparation of alkanol acrylates, oxy ester formation when particular the preparation of n- butyl acrylate and 2-ethylhexyl acrylate, in particular very important.

It is a property of oxyesters that the boiling point of the oxyester exceeds that of the starting acid, the starting alcohol, the ester of interest produced and all organic solvents used as well.

Work-up of all such esterification reaction mixtures is usually carried out by separating unreacted starting compounds and the desired ester from the reaction mixture by distillation, in which case the acid used for the esterification is used. The catalyst can be removed beforehand by extraction, preferably with water and / or alkaline water (eg Ullmann's Encyclopedia
of Industrial Chemistry, No. A1, 5th Edition, VC
H, page 167 et seq.). The residual product remaining during such distillation work-up contains oxyesters, which causes a considerable loss in yield.

For the above reasons, various additional methods have
It has been tested to solve the problems resulting from the formation of oxyesters. In this way, JP-A-57-6222 is used.
No. 9, gazette describes the alkali saponification of high boiling esterification residues. In this way, some of the alcohol used and acrylic acid and β-hydroxypropionic acid or their salts are regenerated. Therefore, a simple and economical return of the product to the esterification reaction is not possible. Japanese Examined Patent Publication No. 47-15936 describes the production of an acrylic acid ester (transesterification reaction) by reacting a β-alkoxypropionic acid ester with acrylic acid in the presence of a strong acid. However, this results in a by-product which cannot be recycled to the esterification reaction and thus an equimolar amount of β-alkoxypropionic acid corresponding to the waste. JP-A-5
-25086 discloses a Michael addition product in the presence of sulfuric acid and an excess of water at elevated temperature, i.e. butyl β-butoxypropionate (where x is 1 and R is a butyl group). (See I)) is described. However, the yield is only about 30%. Finally, JP-A-6-65149 describes the dissociation of Michael addition products I and II (see above, x = y = 1) in the presence of titanium alkoxide. In the case of this reaction, the conversion is likewise low (<60%) and large amounts of titanate are required. Therefore, this method is uneconomical and environmentally damaging because of the large amount of titanate to be discarded.

GB-A-923595 describes the regeneration of monomers from the residue of the esterification of acrylic acid with alkanols in the absence of molecular oxygen. This British patent specification recommends, inter alia, that all volatile monomers be removed prior to dissociation, the dissociation is carried out in the presence of sulfuric acid and the dissociation products are removed using a stream of inert gas. ing. According to the examples of this British patent specification, the dissociation is always carried out at at least 300 ° C. Coke is produced as a residue (17-40
%), And this coke must be dug out of the reactor. Therefore, this method is neither economical nor can it be carried out on an industrial scale. A further drawback is the need for oxygen exclusion.

People's Republic of China Patent Application Publication No. 10636
No. 78 describes the dissociation of alkoxypropionate ester present in the esterification residue in the presence of sulfuric acid in a cascade, in which case the temperature and the catalyst concentration (0.8-1 0.5%) is different for each reactor. Distillation to separate alkanol and acrylate is combined with dissociation. This method is extremely difficult to handle and does not achieve high conversion rates.

Finally, the People's Republic of China Patent Application Publication No. 10
The specification of 58390 describes the dissociation of alkoxypropionic acid ester into an alkanol and an acrylic acid ester in the presence of sulfuric acid. This process is performed in stages. The dissociation is first carried out under reflux and subsequently the reaction product is distilled off. The dissociation of the acrylic acid-containing ester residue from the ethyl / methyl acrylate preparation (ethyl ethoxy propionate, methyl methoxy propionate) is carried out in the presence of ethanol or methanol. As in the case of this patent application of the People's Republic of China, this method is complicated and does not achieve a high conversion rate.

[0014]

The object of the present invention is to carry out the re-dissociation of oxyesters in the abovementioned residue products and to obtain the starting acid, the starting alcohol and this process without the disadvantages of the processes of the prior art. The intended ester is reused for esterification.

[0015]

SUMMARY OF THE INVENTION The above-mentioned problems are solved by removing unreacted starting compound and (meth) acrylic acid ester formed by separation by distillation and obtaining a residue product containing oxyester. In a method of esterifying (meth) acrylic acid with an alkanol in the presence of a silane catalyst, the residual product is separated off and (a) the residual product is directly mixed with (meth) acrylic acid. , And dissociate the oxyester present in the residual product at elevated temperature in the presence of an acid catalyst different from (meth) acrylic acid, or (b) first remove the oxyester from the residual product. Separated by distillation, mixing the distillate with (meth) acrylic acid and at elevated temperature,
It has been found to be solved by a method of esterification of (meth) acrylic acid by dissociation in the presence of an acid catalyst different from (meth) acrylic acid. The alkanol is preferably n-butanol or 2-ethylhexanol. Usually, 5 to 50% by weight of (meth) acrylic acid, in particular in the case of (a) relative to the amount of residue product, or to the amount of distillate in the case of (b), especially 10 to 40 weight%
Is added. (Meth) acrylic acid is usually added in a known form stabilized with a polymerization inhibitor. According to an advantageous embodiment of the invention, the method of dissociation is carried out in the presence of molecular oxygen.

Unlike the dissociation without the addition of (meth) acrylic acid, the process according to the invention results in a reduced production of by-products (dialkyl ethers, olefins).

Moreover, according to an advantageous development of the invention, the residual product is different from (meth) acrylic acid and in addition to the esterifying acid catalyst which may already be present, a mineral acid,
For example, sulfuric acid or phosphoric acid, and alkyl- or aryl sulfonic acids, such as methane sulfonic acid or p.
-Has another acid selected from the group of toluenesulfonic acids. The total amount of acid different from the (meth) acrylic acid present in that case depends on the amount of residual product in the case of (a) or in the case of the distillate in the case of (b). It can be from 1 to 20% by weight, in particular from 5 to 15% by weight. A similar catalytic acid content is advantageous for the dissociation where the oxyester is separated by distillation before the dissociation. A stripping gas, which preferably contains molecular oxygen, is used as an entrainer for the dissociation products either in the residual product in the case of (a) or in the case of (b) obtained from this residual product. It is particularly effective when conducted in the distillate of. Air or a mixture of air and an inert gas (for example nitrogen) is preferably used as stripping gas.

The advantages of the process according to the invention are in particular that the dissociation proceeds more rapidly, less by-products are produced, eg ethers or olefins, and less acidic dissociation catalyst is consumed. is there. Thus, above all, a smaller loss of starting material, in particular alcohol, is obtained compared to the known methods. Moreover, high dissociation yields can be achieved. Direct return of the dissociation mixture does not adversely affect the purity of the (meth) acrylic acid ester and results in a low ether content. For this reason there is a need for uncomplicated separation of ethers from easily polymerisable (meth) acrylic acid esters. In the case of distillative separation of oxyesters from the residual product, the distillation conditions depend on the type of alcohol component used for the esterification. Usually temperature 100-300 ° C
And pressures of 1 to 50 mbar are used. All conventional distillation equipment is suitable for this distillation process. Since only a simple separation operation has to be carried out, a simple splash repellant is usually sufficient, ie a column is usually not necessary.

In order to work up according to the invention the obtained oxyester in the residue product in the case of esterification or the oxyester distillate separated from the esterification residue, a jacket heating device or heating coil is used. A simple heatable stirred reactor provided, or else a forced circulation evaporator in combination with a residence time vessel, such as falling film evaporator or flash evaporator, can be used. To achieve a better separation of the dissociation products from the residual product or the oxyester distillate, it is not possible to use rectification attachments mounted on the dissociator, for example packed or tray columns. , Is advantageous.
Rectification attachments are usually operated by using stabilization with polymerization inhibitors (eg phenothiazine, hydroquinone monoethyl ether, etc.).

The conditions for carrying out the process according to the invention of dissociating the oxyester formed in or separated from the residual product in the case of esterification are as follows: : Mineral acids such as sulfuric acid and phosphoric acid, and (meth)
At least one acid selected from the group consisting of organic acids different from acrylic acid, such as alkyl- or aryl sulfonic acids, such as methane sulfonic acid or p-toluene sulfonic acid Amount of catalyst: residual in the case of (a) The amount of product
Or in the case of (b), from 1 to 20% by weight, especially 5% by weight, based on the amount of oxyester distillate separated from the residual product.
% Of (meth) acrylic acid: relative to the amount of residual product in the case of (a) or in the case of (b) the oxyester distillate separated from the residual product. 5 to 50 for quantity
% By weight, in particular 10-40% by weight Temperature: 150-250 ° C., especially 180-230 ° C. Pressure: stripping gas, preferably at atmospheric pressure or reduced pressure (so that the dissociation products evaporate immediately) (<1 atm) When used: Amount: 1 to 100 l / hour Reaction time: 1 to 10 hours Conversion rate: ≧ 90%.

The reaction is carried out, for example, by continuously removing the residue product to be dissociated from the work-up by distillation of the esterification mixture and feeding it into the dissociation reactor together with the dissociation catalyst. However, the reaction can also be carried out batchwise. Using a semi-continuous reaction procedure in which the product to be dissociated is continuously fed to the dissociation reactor (containing the dissociation catalyst) and the residual product is batchwise removed from the dissociation reactor only after the dissociation is complete It is also possible. The dissociation products are continuously separated by distillation.

The suitability of the dissociation process described above is not limited to a particular type of esterification process in which oxyesters, ie addition compounds I and II, are obtained as by-products. Normal,
Esters are manufactured in the usual way (Ullmann's Encyclopei
da of Industrial Chemistry, No. A1, 5th edition, VC
H, page 167 et seq.).

A typical example of the conditions under which esterification can be carried out prior to the dissociation of the oxyester can be simply expressed as: alcohol: (meth) acrylic acid 1: 0.7- 1.2
(Mol) Catalyst: Sulfuric acid or sulphonic acid Amount of catalyst: 0.1-10% by weight (particularly 0.5-5% by weight) with respect to the starting material Stabilization: Phenothiazine 200-2000 ppm (relative to the weight of the starting material ) Reaction temperature: 80 to 160 ° C, especially 90 to 130 ° C Reaction time: 1 to 10 hours, especially 1 to 6 hours.

If desired, an entraining agent (eg cyclohexane or toluene) can be used to remove the water of esterification. The esterification can be carried out continuously or batchwise under atmospheric pressure, superatmospheric pressure or reduced pressure.

In the case of acid-catalyzed esterification of acrylic acid with alkanols, the esterification acid catalyst, the unreacted starting materials and the residual product obtained after separation of the acrylic ester are usually It has the following composition: Acrylate 1-20% by weight Alkoxypropionate (see formula I) 50-80% by weight Acyloxypropionate (see formula II) 5-30% by weight Remaining: mainly stabilizers (Phenothiazine) and polymers.

Further details and advantages of the invention will now be described in detail by way of example.

First, the results achieved using the method not according to the invention are described by way of comparative examples.

[0028]

【Example】

Comparative Example A glass circulating reactor (capacity: 1 l) heated by a preheating plug does not contain an esterification acid catalyst n
500 g of oxyester distillate obtained from the esterification residue from the butyl acrylate product were charged with 40 g of p-toluenesulfonic acid. The oxyester distillate contains butyl acrylate 11.0% by weight, butoxyester I (R = C ₄ H ₉ ) 64.8% by weight acyloxyester I (R = C ₄ H ₉ ) 20.5% by weight. doing.

The dissociation temperature was 195 ° C. and the working pressure was 1 atm.

Throughout the dissociation, the esterification residue to be dissociated was continuously fed to the dissociation reactor, adjusting the level in the reactor.

The dissociation products are withdrawn in the form of vapor and are placed on a dissociation reactor in a column (50 cm × 2.8 c).
m, cavity). 7401 g of the mixture (62 g / h) were fed to the dissociation reactor over 119.5 h and 7080 g of the dissociation product were condensed.

According to gas chromatographic analysis, the condensate contained the following components: Butyl acrylate 72.0% by weight Butanol 13.9% by weight Acrylic acid 4.8% by weight Dibutyl ether 1.4 % By weight Butene 6.6% by weight Butyl butoxypropionate 0.2% by weight Conversion: 96% by weight based on oxyester.

The dissociation residue was still easily handleable (pumpable) at 25 ° C. and contained no solids.

Example of the process according to the invention In a glass circulation reactor (volume: 1 l) heated by a preheating plug, the oxyester distillate 5 from the comparative example is used.
00 g was charged with 40 g p-toluenesulfonic acid and 150 g acrylic acid (stabilized with phenothiazine 300 ppm).

The dissociation temperature was 195 ° C. and the working pressure was 1 atm.

The oxyester distillate to be dissociated and the corresponding adduct of acrylic acid (30% by weight) were fed continuously to the dissociation reactor, adjusting the level in the reactor. The dissociation products were condensed at the top of a column (50 cm x 2.8 cm, cavity) mounted on the dissociation reactor.

12323 g of oxyester distillate (104 g / h) and 3697 g of stabilized acrylic acid were fed to the dissociation reactor over 118 hours and 15529 g of the product mixture were condensed. According to gas chromatographic analysis, the condensate contained the following components: Butyl acrylate 67.3 wt% Butanol 5.3 wt% Acrylic acid 21.2 wt% Dibutyl ether 0.4 wt% Butene 2.3% by weight Conversion: 97% by weight, based on the oxyester.

[0038]

From the above examples of the process according to the invention, it is possible that this process achieves a higher conversion and a smaller loss of starting material than in the case of the known processes. I understand.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication C07C 67/54 C07C 67/54 // C07B 61/00 300 C07B 61/00 300 C07C 57/04 2115 -4H C07C 57/04 (72) Inventor Heinrich Aichinger Mannheim Hans-Sachsring, Federal Republic of Germany 16 (72) Inventor Holger Helpst, Germany Frankenthal Rudolf Strasse 7 Ar (72) Inventor Nicole E. McGron United States Texas Friends Wood Bisonson 2231 (72) Inventor Jerry W. Darlington United States Illinois Marengo Bath Coat 20613 (72) Inventor Calvin Ef Donat Amelie United States Texas Lake Ja Kuson Dea Trail 106 (72) inventor John Sea Hyman United States Texas West Columbia Seminole rain 14

Claims (1)

[Claims] 1. An alkanol in the presence of an esterification catalyst by separating off by distillation the unreacted starting compound and the formed (meth) acrylic acid ester and obtaining a residual product containing oxyester. In the method of esterifying (meth) acrylic acid with the use of (a) separating and removing the residual product, and (a) mixing the residual product directly with (meth) acrylic acid, and The oxyester present in the product is dissociated at elevated temperature in the presence of an acid catalyst different from (meth) acrylic acid, or (b) the oxyester is first separated from the residual product by distillation and distilled A substance is mixed with (meth) acrylic acid, and dissociates at an elevated temperature in the presence of an acid catalyst different from (meth) acrylic acid.
(Meth) acrylic acid esterification method.